1. Field of the Invention
The present invention relates to a wireless transmitting method and a wireless transmitter which are preferably applied to the case where a wireless signal is transmitted to various devices to form a local area network (LAN) between a plurality of devices, for example.
2. Description of the Related Art
As a packet structure for asynchronous transmission, a method of distinguishing between a header information portion and a data payload portion to build one packet is disclosed in Japanese Laid-Open Patent Publication No. H11-215136.
According to the above invention, only a portion included in common header information is first decoded before all the packets for asynchronous transmission are decoded to make decidable of the presence to make decidable of contents of the data payload portion following the header portion.
Furthermore, there has also been proposed a method of carrying out transmission by including length information of the data payload portion in the common header information portion.
FIG. 16 is a diagram showing an example of a wireless transmission frame structure according to a conventional method. Although a frame is herein defined for convenience, such a frame structure is not always required. In the drawing, a transmission frame arriving in a fixed transmission frame cycle 160 is defined, and a management information transmitting region 161 and an information transmitting region 162 are provided therein.
A down management information transmission interval (DM Down Link Management) 163 for notifying a frame cycle and network common information is provided at the head of the frame. Subsequently, a station sync transmitting interval (UM: Up Link Management) 164 is provided. There has been supposed such a structure that DM forms a down management interval (frame synchronizing area) including frame synchronizing information, and UM forms a station synchronizing interval (node synchronizing area), which are assigned respectively to each communicating station forming a network to prevent the conflict of transmission by a plurality of communicating stations.
For example, by receiving all portions other than a transmitting portion of a local station in the station synchronizing interval, a connection link state with a communicating station present around the local station can be grasped.
Moreover, by reporting to each other the status of the connection link in the information transmitted on the station synchronizing interval of the local station in the next frame, the connection status of the network can be grasped by each communicating station.
The information transmitting region 162 consists of a band reservation transmitting region 165 to be set if necessary and an asynchronous transmitting area 166 in the other portion.
In other words, if the band reservation transmission is not required, all the information transmitting region can be transmitted as asynchronous transmitting area.
By taking such a frame structure, isochronous (Isochronous) transmission defined by e.g. IEEE 1394, is carried out in the band reservation transmitting area and asynchronous transmission or the like is carried out in the asynchronous transmitting area.
There has been proposed a first conventional wireless transmitting method in which when a header information portion to be decoded earlier including information about the presence of a data payload portion is transmitted succeeding data payload portions are partitioned by the fixed length for transmission, whereby transmission control can be carried out by the fixed-length block unit, so that retransmission control in a wireless interval can easily be processed by the fixed unit.
By partitioning one packet by the fixed length unit in this manner, processing to decode in a communicating station on the receiving side can be simplified.
FIG. 17 is a diagram showing an example of a wireless transmission packet structure according to the first conventional method. In FIG. 17, there is shown an example of a packet structure in which information is divided by the predetermined transmission data payload 172 to each of which a preamble 170 and header information 171 are added for transmission according to the first conventional method.
In the drawing, an information string to be transmitted is divided by the fixed-length data payload 172 thereby making a packet to be built. In other words, there are a plurality of preambles 170 and the header information 171, so that if the preamble 170 is great, a transmission efficiency will deteriorate.
A second conventional wireless transmitting method has been proposed in which, when the header information portion to be decoded earlier including size (length) information of the data payload portion is transmitted, length information of the data payload portion can be specified in advance, thereby making it possible to continuously carry out processings to transmit and receive one packet for asynchronous transmission.
According to this method, there has been an advantage that the asynchronous transmission packet can be built without carrying out a fragment processing of a transmission packet.
Moreover, FIG. 18 is a diagram showing an example of a wireless transmission packet structure according to the second conventional method. In FIG. 18, there is shown an example of the structure of a packet to be transmitted, in which an information string to be transmitted is not divided but a data payload 182 is formed as one block, to which a preamble 180 and header information 181 are added according to the second conventional method.
As shown in the drawing, the processing to divide by the unit is not required as described above but the header information 181 including information on the packet length should be transmitted. This means that, a long packet includes only one preamble 180 and only one header information 181, so that missing no information to be received.